The invention relates to a color display device and more particularly to a liquid crystal color display device.
The current trend, for the generation of large-sized video images, is towards the use of liquid crystal active matrices (LCD screens) in projection devices.
The projection of color images can be achieved either with three LCD screens, each illuminated by one of the three primary components, namely the red, green or blue (R, G, B) components, or with a single trichromatic LCD screen which is then provided with colored filters.
The integration of R, G, B colored filters into the structure of an LCD screen enables the making of color image projection devices whose design is simple because they are formed by only one source and only one LCD screen. These so-called "monovalve" projection devices are nevertheless limited, at present, to the projection of poor-quality, low-resolution images because of the following drawbacks:
--low light efficiency related to the spatial distribution of these colored filters which divide the effective transmission of the LCD screen by three;
--the non-negligible absorption of the colored filters furthermore limits the power of the light sources that can be used with these screens;
--the technological cost entailed by the making of these screens is high: it arises firstly from the implementation of these filters in the liquid crystal cell and, secondly, from a density of picture elements (pixels) that is greater for color screens than it is for monochromatic screens if they are to be made in reasonable dimensions (&lt;6 inches diagonally).
The device according to the invention can be used to make an LCD monovalve projector whose light efficiency is greater than that of the usual devices. The expected theoretical gain is 3 to 6. This device implements a particularly compact structure to achieve the R, G, B color illumination of the LCD screen of a monovalve projector. The advantages of this device may be described as follows:
--the elimination of the technological steps for the making of the colored filters for trichomatic video-controlled LCD screens: the chromatic separation is obtained by a grating-type function;
--the improvement of the light efficiency of projection through the function of the focusing of the illumination white source in the pixels of the LCD screen: an array of cylindrical micro-lenses attached to the front face of the LCD screens can be used to generate R, G, B colored lines that are focused in one dimension in the plane of the liquid crystal;
--the pre-filtering of the source and the matching of the section of the illumination beam to the 16/9 rectangular format of the LCD screen can be achieved simultaneously through the chromatic separation component.